A cellular communication system can include a number of roaming, automobile-mounted or handheld telephone sets which are served by either fixed, ground-based stations or by orbiting satellites or by a combination of both. The capacity of such systems to serve a large number of subscribers depends on how much of the radio spectrum is allocated for the service and how efficiently the radio spectrum is used. Efficiency of spectral utilization is measured in units of simultaneous conversations (erlangs) per megahertz per square kilometer. In general, spectral efficiency can be improved more by finding ways to re-use the available bandwidth many times over than by attempting to pack more conversations into the same bandwidth, since narrowing the bandwidth generally results in the need to increase spatial separation between conversations thus negating the gain in capacity. Therefore, it is generally better to increase the bandwidth used for each conversation so that closer frequency re-use is possible.
One method to increase the capacity is to use a phased array communications satellite to relay signals from ground stations to a plurality of mobile stations. A ground-controlled orbiting phased array system is disclosed in U.S. patent application Ser. No. 08/179,953, filed Jan. 11, 1994, and U.S. patent application Ser. No. 08/179,947, filed Jan. 11, 1994, now U.S. Pat. No. 5,574,967, both of which are expressly incorporated herein by reference.
The prior art does not disclose the use of coherent time-multiplexed feeder links with distributed demultiplexing for reducing the cabling to a deployable phased array. Some prior art systems have separate coaxial cables or waveguides connecting each element of the array to a centrally located transponder. This arrangement was adequate for prior art systems in which the number of antenna elements or beams to be created was small, for example, 6, 19, or 37, but becomes impractical for the number of elements or beams envisioned in the present invention. One embodiment of the present invention eliminates the multiplicity of feeder cables reducing the weight of the system considerably.
Another problem with traditional satellite communication system is the limited amount of power in the satellite which is available for communication purposes. In order to combat this problem, traditional communication satellites employ solar panels to convert sunlight into energy. However, the power provided by the solar panels is sometimes not enough. Thus, there is a need for a method for providing additional power to a satellite.